Mr. Menino still has nine months to go in his fifth term as mayor, and his two decades on the job makes him one of America’s longest-serving big-city mayors. During a tenure free of major scandals, he presided over an era of economic revitalization and falling crime rates, and helped burnish the city’s image as an attractive place to live as well as work.

“Boston is the vibrant, welcoming, and world-class city it is today because of Tom Menino,” President Obama said in a statement about the news. “His efforts to revitalize neighborhoods, schools, and businesses, better integrate police officers into their communities, and reduce gun violence, [have] charted Boston on a course for a better future.”

Known for slurring his words rather than for adroit oratory, he surprised many with his staying power.

Some critics initially said he lacked vision. He earned the nickname “urban mechanic” for what seemed to be a small-bore focus on things like fixing streets or adding bike lanes. Amid a construction boom, Menino never met a ribbon cutting he didn’t like.

But to him, little efforts were part of something big.

"What is a vision?" Menino asked in a 1994 Boston Globe profile. "Sometimes we get caught up in the grandiose. My vision is jobs, a better school system, community policing, health care. When I leave this job, I want the city to be in better shape than when I took it over."

The work remains unfinished – perhaps why Menino pondered the idea of seeking a sixth term.

Whoever succeeds him will have more work to do to improve the city’s schools, transportation, and economic opportunities.

And for his part, Menino pledged to stay involved. “I am not retiring, but just turning one page,” he said.